Drop shebangs from bug_report and test scripts

At least `[[ ]]` and arrays are not Posix shell compatible.
And anyway it is better to run the scripts by default using
the current SHELL.

The only exception is `test/runner` that uses bash by default,
as it is normally used via make that uses /bin/sh otherwise.
Merge pull request #84 from tmatilai/non-posix-sh

Use bash in scripts and tests